Isaiah 57:5

Inflaming yourselves with idols under every green tree Or, "inflamed with or among oaks" F8; with images made of oaken wood, such as the Papists worship, ( Revelation 9:20 ) expressing a burning zeal for their idols, and being as hot upon them, as impure persons burn in lust one towards another: or "with mighty ones" F9; the kings and potentates of the earth, with whom the whore of Rome commits her fornication, even in every flourishing kingdom and state in Europe, compared to a green tree; alluding to the custom of the Heathens, who used to set up their idols under green trees and groves, and there worship them, which were pleasing to the flesh; and I wish, says Musculus on the text, there were no instances of this kind in the Papacy. Slaying the children in the valleys, under the clifts of the rocks? this may refer to the cruelty of these idolatrous worshippers; for, as they burn with zeal to their idols, so with rage against those that oppose their idolatrous practices, not sparing men, women, and children; and such butcheries have been committed in many places, and especially in the "valleys" of Piedmont; nor could the cragged rocks secure them from their falling a sacrifice unto them. Or it may intend the ruining and destroying the souls of such, who, before they fell into their hands, were innocent as children, by their superstitious worship and idolatry, committed in low and dark places, under cragged rocks, and in caves and dens; such as the above mentioned commentator speaks of, a very dark one, under a prominent rock, in which the ignorant and unhappy people, some time ago, worshipped and invoked a certain blessed saint, he knew not who, which could scarce be looked into without horror; and such was the cave in which they worshipped the angel Michael.